Optimal cancer therapy is designed to exert maximal effect on tumor cells while having minimal side-effects on normal cells. Unfortunately this goal is difficult to achieve due to a pack of specificity for the cancer cells. Remarkable advances in our understanding of the molecular biology of cancer has provided possible avenues for more successful 'targeted' cancer treatment. Several crucial oncoprotein interactions occur exclusively in tumor cells and thus provide ideal targets for intervention. The proposed project is to develop a model system for a target specific therapy of leukemia cells. We have chosen to targeted the interaction of two oncoproteins, LMO2 and SCL/TAL1 in the search for inhibitors. A genetic selection will be used to identify random, constrained peptide sequences which are capable of blocking these interactions and which do not interfere with other interactions involving the SCL protein. This technique termed 'dual-bait/reporter reverse two hybrid screening' allows one to select for against specific blockers of known interactions in yeast cells. This procedure will be most suitable for high through-put drug screening projects, since the test for specificity can be readily performed without recourse to plasmid rescue, or yeast mating. This technique will be applied to the screening of random peptide libraries and peptide libraries derived from natural sources. The affinity and specificity of the interaction blockers derived from the screen will be determined by both genetic and physical approaches, using the novel 'dual-bait/reporter' system and by surface plasmon resonance experiments. Finally, the validity of this approach will be established by measuring the efficacy of selected peptide inhibitors in inhibiting the growth of leukemia cells.